The present invention relates to a resin-molded lens for a lamp, and particularly to a resin-molded lens in which depressions (so-called sink marks) are prevented from being formed in the surface of a lens surface portion.
Recently, lenses for automotive lamps have been formed as resin moldings. For example, as shown in FIG. 1, a lens 1 used for a rear lamp of a car is formed of resin material. In such a lens 1, a lens surface portion for transmitting light from a lamp is generally thin. A seal leg portion 5 is formed on the circumference of the lens surface portion so that the lens can be attached to a lamp body to thereby form a seal therebetween through the seal leg portion 5. Boss portions 6 through which pass screws for fixing the lens to the lamp body are provided in positions of the seal leg portion 5. For this purpose, the boss portions 6 are made generally thick.
A resin-molded lens having such a structure is formed by integral molding of resin. However, sometimes one or more depressions, called sink marks, are generated in the surface of the lens because of shrinkage when the injected resin cools and solidifies. Such sink marks are conspicuous in proportion to the volume of the resin. In a lens as described above, a sink mark is apt to be formed in thick portions having a large volume of resin such as the seal leg portion or the boss portions. In particular, the boss portions are large in volume in comparison with other portions, so that a sink mark X is often formed in the surface of the lens surface portion 2 corresponding to each boss portion 6, as shown in FIG. 5(a), which shows an enlarged sectional structure of the portion taken on line A--A in FIG. 1. Although such a sink mark cause no problem as to the optical function of the lens, it is not desirable in that the external appearance of the lamp is degraded.